I mow a few bumpy yards including my own. Last year my mower started missing and generally running rough. I was about to switch it off when I noticed the air filter shaking. Yep, the bolts worked loose on the intake manifold. It was fine the rest of the year. This year, my volume doubled and I still have to do my own bumpy yard. I remember having to tighten those bolts up at the beginning of this season. Also, when I first crank it up, white smoke comes out of the exhaust and it generally ran less than perfect. Yesterday, I was about 95% finished with my yard when it started coughing again and I saw the filter shake. I got it up to the driveway and tightened up the bolts. I guess shaking in the loose position made the bottom one mess up because I stripped it real easy. It was 5:10 and I knew all the mower shops would be closed sat because of the holiday. I remembered Helicoil! I got on the net and can now proclaim I am as close to an expert as you can get! Anyway, I got up this morning and searched all over town. Either the stores were closed or they could order it and have it by tuesday. I was heading to a shop that occured to me might be open when I stopped at a traffic light. There next to me on the left was an O'Reilly auto parts. I checked and they had it. 1/4x20-$34.99. I love Helicoil. Why don't these manufacturers just install them from the get go? I know I'll never have a problem with my manifold again. I did both bolt holes! Seriously though, my google search brought up all kinds of machinery for assembly lines and such. It would really be nice to know your bolts are screwed into stainless steel and not just soft aluminum. I forgot to add, the gasket had about 1/2 inch missing so I went over to the boneyard and got one off a basket case. That's probably why it smoked. It don't smoke anymore and runs like a new engine.